Summary: Nested Classes | Ctors | Methods | Inherited Methods

FragmentStateAdapter

Kotlin |Java

public abstract class FragmentStateAdapter
extends Adapter<FragmentViewHolder> implements StatefulAdapter

java.lang.Object
↳	androidx.recyclerview.widget.RecyclerView.Adapter<androidx.viewpager2.adapter.FragmentViewHolder>
	↳	androidx.viewpager2.adapter.FragmentStateAdapter

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Similar in behavior to FragmentStatePagerAdapter

Lifecycle within RecyclerView:

• RecyclerView.ViewHolder initially an empty FrameLayout, serves as a re-usable container for a Fragment in later stages.
• RecyclerView.Adapter.onBindViewHolder(VH, int) we ask for a Fragment for the position. If we already have the fragment, or have previously saved its state, we use those.
• RecyclerView.onAttachedToWindow() we attach the Fragment to a container.
• RecyclerView.Adapter.onViewRecycled(VH) we remove, save state, destroy the Fragment.

Summary

Nested classes
class	FragmentStateAdapter.FragmentTransactionCallback Callback interface for listening to fragment lifecycle changes that happen inside the adapter.

Public constructors
FragmentStateAdapter(FragmentActivity fragmentActivity)
FragmentStateAdapter(Fragment fragment)
FragmentStateAdapter(FragmentManager fragmentManager, Lifecycle lifecycle)

Public methods
boolean	containsItem(long itemId) Default implementation works for collections that don't add, move, remove items.
abstract Fragment	createFragment(int position) Provide a new Fragment associated with the specified position.
long	getItemId(int position) Default implementation works for collections that don't add, move, remove items.
void	onAttachedToRecyclerView(RecyclerView recyclerView) Called by RecyclerView when it starts observing this Adapter.
final void	onBindViewHolder(FragmentViewHolder holder, int position) Called by RecyclerView to display the data at the specified position.
final FragmentViewHolder	onCreateViewHolder(ViewGroup parent, int viewType) Called when RecyclerView needs a new RecyclerView.ViewHolder of the given type to represent an item.
void	onDetachedFromRecyclerView(RecyclerView recyclerView) Called by RecyclerView when it stops observing this Adapter.
final boolean	onFailedToRecycleView(FragmentViewHolder holder) Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state.
final void	onViewAttachedToWindow(FragmentViewHolder holder) Called when a view created by this adapter has been attached to a window.
final void	onViewRecycled(FragmentViewHolder holder) Called when a view created by this adapter has been recycled.
void	registerFragmentTransactionCallback(FragmentStateAdapter.FragmentTransactionCallback callback) Registers a FragmentStateAdapter.FragmentTransactionCallback to listen to fragment lifecycle changes that happen inside the adapter.
final void	restoreState(Parcelable savedState) Restores adapter state
final Parcelable	saveState() Saves adapter state
final void	setHasStableIds(boolean hasStableIds) Indicates whether each item in the data set can be represented with a unique identifier of type Long.
void	unregisterFragmentTransactionCallback(FragmentStateAdapter.FragmentTransactionCallback callback) Unregisters a FragmentStateAdapter.FragmentTransactionCallback.

Inherited methods
From class androidx.recyclerview.widget.RecyclerView.Adapter final void bindViewHolder(FragmentViewHolder holder, int position) This method internally calls onBindViewHolder(ViewHolder, int) to update the RecyclerView.ViewHolder contents with the item at the given position and also sets up some private fields to be used by RecyclerView. final FragmentViewHolder createViewHolder(ViewGroup parent, int viewType) This method calls onCreateViewHolder(ViewGroup, int) to create a new RecyclerView.ViewHolder and initializes some private fields to be used by RecyclerView. int findRelativeAdapterPositionIn(Adapter<? extends RecyclerView.ViewHolder> adapter, RecyclerView.ViewHolder viewHolder, int localPosition) Returns the position of the given RecyclerView.ViewHolder in the given RecyclerView.Adapter. abstract int getItemCount() Returns the total number of items in the data set held by the adapter. long getItemId(int position) Return the stable ID for the item at position. int getItemViewType(int position) Return the view type of the item at position for the purposes of view recycling. final RecyclerView.Adapter.StateRestorationPolicy getStateRestorationPolicy() Returns when this Adapter wants to restore the state. final boolean hasObservers() Returns true if one or more observers are attached to this adapter. final boolean hasStableIds() Returns true if this adapter publishes a unique long value that can act as a key for the item at a given position in the data set. final void notifyDataSetChanged() Notify any registered observers that the data set has changed. final void notifyItemChanged(int position, Object payload) Notify any registered observers that the item at position has changed with an optional payload object. final void notifyItemChanged(int position) Notify any registered observers that the item at position has changed. final void notifyItemInserted(int position) Notify any registered observers that the item reflected at position has been newly inserted. final void notifyItemMoved(int fromPosition, int toPosition) Notify any registered observers that the item reflected at fromPosition has been moved to toPosition. final void notifyItemRangeChanged(int positionStart, int itemCount, Object payload) Notify any registered observers that the itemCount items starting at position positionStart have changed. final void notifyItemRangeChanged(int positionStart, int itemCount) Notify any registered observers that the itemCount items starting at position positionStart have changed. final void notifyItemRangeInserted(int positionStart, int itemCount) Notify any registered observers that the currently reflected itemCount items starting at positionStart have been newly inserted. final void notifyItemRangeRemoved(int positionStart, int itemCount) Notify any registered observers that the itemCount items previously located at positionStart have been removed from the data set. final void notifyItemRemoved(int position) Notify any registered observers that the item previously located at position has been removed from the data set. void onAttachedToRecyclerView(RecyclerView recyclerView) Called by RecyclerView when it starts observing this Adapter. abstract void onBindViewHolder(FragmentViewHolder holder, int position) Called by RecyclerView to display the data at the specified position. void onBindViewHolder(FragmentViewHolder holder, int position, List<Object> payloads) Called by RecyclerView to display the data at the specified position. abstract FragmentViewHolder onCreateViewHolder(ViewGroup parent, int viewType) Called when RecyclerView needs a new RecyclerView.ViewHolder of the given type to represent an item. void onDetachedFromRecyclerView(RecyclerView recyclerView) Called by RecyclerView when it stops observing this Adapter. boolean onFailedToRecycleView(FragmentViewHolder holder) Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state. void onViewAttachedToWindow(FragmentViewHolder holder) Called when a view created by this adapter has been attached to a window. void onViewDetachedFromWindow(FragmentViewHolder holder) Called when a view created by this adapter has been detached from its window. void onViewRecycled(FragmentViewHolder holder) Called when a view created by this adapter has been recycled. void registerAdapterDataObserver(RecyclerView.AdapterDataObserver observer) Register a new observer to listen for data changes. void setHasStableIds(boolean hasStableIds) Indicates whether each item in the data set can be represented with a unique identifier of type Long. void setStateRestorationPolicy(RecyclerView.Adapter.StateRestorationPolicy strategy) Sets the state restoration strategy for the Adapter. void unregisterAdapterDataObserver(RecyclerView.AdapterDataObserver observer) Unregister an observer currently listening for data changes.
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait(long arg0, int arg1) final void wait(long arg0) final void wait()
From interface androidx.viewpager2.adapter.StatefulAdapter abstract void restoreState(Parcelable savedState) Restores adapter state abstract Parcelable saveState() Saves adapter state

Public constructors

FragmentStateAdapter

public FragmentStateAdapter (FragmentActivity fragmentActivity)

Parameters
fragmentActivity	FragmentActivity: if the ViewPager2 lives directly in a FragmentActivity subclass.

See also:

• FragmentStateAdapter(Fragment)
• FragmentStateAdapter(FragmentManager, Lifecycle)

FragmentStateAdapter

public FragmentStateAdapter (Fragment fragment)

Parameters
fragment	Fragment: if the ViewPager2 lives directly in a Fragment subclass.

See also:

• FragmentStateAdapter(FragmentActivity)
• FragmentStateAdapter(FragmentManager, Lifecycle)

FragmentStateAdapter

public FragmentStateAdapter (FragmentManager fragmentManager, 
                Lifecycle lifecycle)

Parameters
fragmentManager	FragmentManager: of ViewPager2's host
lifecycle	Lifecycle: of ViewPager2's host

See also:

• FragmentStateAdapter(FragmentActivity)
• FragmentStateAdapter(Fragment)

Public methods

containsItem

public boolean containsItem (long itemId)

Default implementation works for collections that don't add, move, remove items.

When overriding, also override getItemId(int)

Parameters
itemId	long

Returns
boolean

createFragment

public abstract Fragment createFragment (int position)

Provide a new Fragment associated with the specified position.

The adapter will be responsible for the Fragment lifecycle:

• The Fragment will be used to display an item.
• The Fragment will be destroyed when it gets too far from the viewport, and its state will be saved. When the item is close to the viewport again, a new Fragment will be requested, and a previously saved state will be used to initialize it.

Parameters
position	int

Returns
Fragment

See also:

• ViewPager2.setOffscreenPageLimit(int)

getItemId

public long getItemId (int position)

Default implementation works for collections that don't add, move, remove items.

When overriding, also override containsItem(long).

If the item is not a part of the collection, return RecyclerView.NO_ID.

Parameters
position	int: Adapter position

Returns
long	stable item id RecyclerView.Adapter.hasStableIds()

onAttachedToRecyclerView

public void onAttachedToRecyclerView (RecyclerView recyclerView)

Called by RecyclerView when it starts observing this Adapter.

Keep in mind that same adapter may be observed by multiple RecyclerViews.

Parameters
recyclerView	RecyclerView: The RecyclerView instance which started observing this adapter.

onBindViewHolder

public final void onBindViewHolder (FragmentViewHolder holder, 
                int position)

Called by RecyclerView to display the data at the specified position. This method should update the contents of the RecyclerView.ViewHolder.itemView to reflect the item at the given position.

Note that unlike ListView, RecyclerView will not call this method again if the position of the item changes in the data set unless the item itself is invalidated or the new position cannot be determined. For this reason, you should only use the position parameter while acquiring the related data item inside this method and should not keep a copy of it. If you need the position of an item later on (e.g. in a click listener), use RecyclerView.ViewHolder.getBindingAdapterPosition() which will have the updated adapter position. Override onBindViewHolder(ViewHolder, int, List) instead if Adapter can handle efficient partial bind.

Parameters
holder	FragmentViewHolder: The ViewHolder which should be updated to represent the contents of the item at the given position in the data set.
position	int: The position of the item within the adapter's data set.

onCreateViewHolder

public final FragmentViewHolder onCreateViewHolder (ViewGroup parent, 
                int viewType)

Called when RecyclerView needs a new RecyclerView.ViewHolder of the given type to represent an item.

This new ViewHolder should be constructed with a new View that can represent the items of the given type. You can either create a new View manually or inflate it from an XML layout file.

The new ViewHolder will be used to display items of the adapter using onBindViewHolder(ViewHolder, int, List). Since it will be re-used to display different items in the data set, it is a good idea to cache references to sub views of the View to avoid unnecessary View.findViewById(int) calls.

Parameters
parent	ViewGroup: The ViewGroup into which the new View will be added after it is bound to an adapter position.
viewType	int: The view type of the new View.

Returns
FragmentViewHolder	A new ViewHolder that holds a View of the given view type.

onDetachedFromRecyclerView

public void onDetachedFromRecyclerView (RecyclerView recyclerView)

Called by RecyclerView when it stops observing this Adapter.

Parameters
recyclerView	RecyclerView: The RecyclerView instance which stopped observing this adapter.

onFailedToRecycleView

public final boolean onFailedToRecycleView (FragmentViewHolder holder)

Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state. Upon receiving this callback, Adapter can clear the animation(s) that effect the View's transient state and return true so that the View can be recycled. Keep in mind that the View in question is already removed from the RecyclerView.

In some cases, it is acceptable to recycle a View although it has transient state. Most of the time, this is a case where the transient state will be cleared in onBindViewHolder(ViewHolder, int) call when View is rebound to a new position. For this reason, RecyclerView leaves the decision to the Adapter and uses the return value of this method to decide whether the View should be recycled or not.

Note that when all animations are created by RecyclerView.ItemAnimator, you should never receive this callback because RecyclerView keeps those Views as children until their animations are complete. This callback is useful when children of the item views create animations which may not be easy to implement using an RecyclerView.ItemAnimator.

You should never fix this issue by calling holder.itemView.setHasTransientState(false); unless you've previously called holder.itemView.setHasTransientState(true);. Each View.setHasTransientState(true) call must be matched by a View.setHasTransientState(false) call, otherwise, the state of the View may become inconsistent. You should always prefer to end or cancel animations that are triggering the transient state instead of handling it manually.

Parameters
holder	FragmentViewHolder: The ViewHolder containing the View that could not be recycled due to its transient state.

Returns
boolean	True if the View should be recycled, false otherwise. Note that if this method returns true, RecyclerView will ignore the transient state of the View and recycle it regardless. If this method returns false, RecyclerView will check the View's transient state again before giving a final decision. Default implementation returns false.

onViewAttachedToWindow

public final void onViewAttachedToWindow (FragmentViewHolder holder)

Called when a view created by this adapter has been attached to a window.

This can be used as a reasonable signal that the view is about to be seen by the user. If the adapter previously freed any resources in onViewDetachedFromWindow those resources should be restored here.

Parameters
holder	FragmentViewHolder: Holder of the view being attached

onViewRecycled

public final void onViewRecycled (FragmentViewHolder holder)

Called when a view created by this adapter has been recycled.

A view is recycled when a RecyclerView.LayoutManager decides that it no longer needs to be attached to its parent RecyclerView. This can be because it has fallen out of visibility or a set of cached views represented by views still attached to the parent RecyclerView. If an item view has large or expensive data bound to it such as large bitmaps, this may be a good place to release those resources.

RecyclerView calls this method right before clearing ViewHolder's internal data and sending it to RecycledViewPool. This way, if ViewHolder was holding valid information before being recycled, you can call RecyclerView.ViewHolder.getBindingAdapterPosition() to get its adapter position.

Parameters
holder	FragmentViewHolder: The ViewHolder for the view being recycled

registerFragmentTransactionCallback

public void registerFragmentTransactionCallback (FragmentStateAdapter.FragmentTransactionCallback callback)

Registers a FragmentStateAdapter.FragmentTransactionCallback to listen to fragment lifecycle changes that happen inside the adapter.

Parameters
callback	FragmentStateAdapter.FragmentTransactionCallback: Callback to register

restoreState

public final void restoreState (Parcelable savedState)

Restores adapter state

Parameters
savedState	Parcelable

saveState

public final Parcelable saveState ()

Saves adapter state

Returns
Parcelable

setHasStableIds

public final void setHasStableIds (boolean hasStableIds)

Indicates whether each item in the data set can be represented with a unique identifier of type Long.

Parameters
hasStableIds	boolean: Whether items in data set have unique identifiers or not.

unregisterFragmentTransactionCallback

public void unregisterFragmentTransactionCallback (FragmentStateAdapter.FragmentTransactionCallback callback)

Unregisters a FragmentStateAdapter.FragmentTransactionCallback.

Parameters
callback	FragmentStateAdapter.FragmentTransactionCallback: Callback to unregister

See also:

• registerFragmentTransactionCallback(FragmentStateAdapter.FragmentTransactionCallback)